Method for controlling downlink transmission power and apparatus for same

ABSTRACT

A method is described for performing power control by a first base station in a wireless communication system. A parameter value related with signal strength of a second base station is acquired. An upper power limit of the first base station is determined in consideration of the signal strength of the second base station. Signal transmission is performed in consideration of the upper power limit of the first base station. If a first condition(s) including that the parameter value is equal to or more than a first threshold value is satisfied, the upper power limit of the first base station is given as an intermediate value. If a second condition(s) including that the parameter value is less than the first threshold value is satisfied, the upper power limit of the first base station is given as a pre-determined value related with the transmit power of the first base station.

This application is a Continuation of co-pending U.S. application Ser.No. 13/638,553 filed Sep. 28, 2012, which is a National Phase ofPCT/KR2011/007475 filed on Oct. 10, 2011, which claims the benefit under35 U.S.C. §119(e) to U.S. Provisional Application No. 61/391,674 filedon Oct. 10, 2010. The contents of all of these applications are herebyexpressly incorporated by reference as fully set forth herein, in theirentirety.

BACKGROUND OF THE INVENTION

Generally, a wireless communication system is developing to diverselycover a wide range to provide such a communication service as an audiocommunication service, a data communication service and the like. Thewireless communication is a sort of a multiple access system capable ofsupporting communications with multiple users by sharing availablesystem resources (e.g., bandwidth, transmit power, etc.). For examplesof the multiple access system, there are CDMA (code division multipleaccess) system, FDMA (frequency division multiple access) system, TDMA(time division multiple access) system, OFDMA (orthogonal frequencydivision multiple access) system, SC-FDMA (single carrier frequencydivision multiple access) system and the like.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an apparatus forcontrolling a downlink transmission power in a wireless communicationsystem and method thereof that substantially obviate one or moreproblems due to limitations and disadvantages of the related art.

One object of the present invention is to provide an apparatus forcontrolling a downlink transmission power of a home base station in aheterogeneous network.

Technical tasks obtainable from the present invention are non-limitedthe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

According to an aspect of the present invention, A method for performingpower control by a home base station in a wireless communication system,the method comprising: acquiring information on downlink signal strengthof a macro cell; and determining an upper limit of downlink transmissionpower of the home base station in consideration of the downlink signalstrength of the macro cell, wherein if a certain condition is satisfied,the upper limit of downlink transmission power of the home base stationis given as an intermediate value among a minimum transmission powervalue, a maximum transmission power value, and a power control valueproportional to the downlink signal strength of the macro cell, whereinif the certain condition is not satisfied, the upper limit of downlinktransmission power of the home base station is given as a certain fixedvalue, and wherein the certain condition includes that a valueindicating the downlink signal strength of the macro cell is equal to ormore than a first threshold value.

According to other aspect of the present invention, A home base stationconfigured to perform power control in a wireless communication system,the home base station comprising: a radio frequency (RF) unit; and aprocessor, wherein the processor is configured to acquire information ondownlink signal strength of a macro cell, and to determine an upperlimit of the downlink transmission power of the home base station inconsideration of the downlink signal strength of the macro cell, whereinif a certain condition is satisfied, the upper limit of downlinktransmission power of the home base station is given as an intermediatevalue among a minimum transmission power value, a maximum transmissionpower value, and a power control value proportional to the downlinksignal strength of the macro cell, wherein if the certain condition isnot satisfied, the upper limit of downlink transmission power of thehome base station is given as a certain fixed value, and wherein thecertain condition includes that a value indicating the downlink signalstrength of the macro cell is equal to or more than a first thresholdvalue.

Preferably, the acquiring the information includes receiving ameasurement report on the downlink signal of the macro cell from a userequipment.

Preferably, the acquiring the information includes measuring thedownlink signal of the macro cell at the home base station.

Preferably, the power control value (P′) is given by following Equation:

P′=α×P _(—) M+β

where, P_M represents a parameter related to the downlink signalstrength of the macro cell,

α represents a positive value, and

β a represents a correction value for power control.

Preferably, the processor is further configured to further to performdownlink transmission, and wherein the transmission power of thedownlink transmission is equal or less than the upper limit of downlinktransmission power of the home base station.

Preferably, if a value indicating uplink signal strength of a macro userequipment is equal to or more than a second threshold value, the powercontrol value is decreased in consideration the uplink signal strength,and if the value indicating the uplink signal strength of the macro userequipment is less than the second threshold value, the power controlvalue is maintained as it is.

Preferably, if a value indicating uplink signal strength of a macro userequipment is equal to or more than a second threshold value, the maximumtransmission power value is decreased in consideration of the uplinksignal strength, and if the value indicating the uplink signal strengthof the macro user equipment is less than the second threshold value, themaximum transmission power value is maintained as it is.

Accordingly, the present invention may be able to control a downlinktransmission power in a wireless communication system. In particular,the present invention may be able to efficiently control a downlinktransmission power of a home base station in a heterogeneous network.

Effects obtainable from the present invention may be non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a diagram for one example of a structure of a radio frame;

FIG. 2 is a diagram for one example of a resource grid of a downlink(hereinafter abbreviated DL) slot;

FIG. 3 is a diagram for a structure of a DL frame;

FIG. 4 is a diagram for one example of a structure of an uplink(hereinafter abbreviated UL) subframe;

FIG. 5 is a diagram for one example of mapping PUCCH format to PUCCHregion physically;

FIG. 6 is a diagram for one example of a power control method in aheterogeneous network according to a related art;

FIG. 7 and FIG. 8 are diagrams for a method of controlling a poweraccording to one embodiment of the present invention; and

FIG. 9 is a diagram for one example of a base station and a userequipment applicable to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

First of all, embodiments of the present invention are usable forvarious wireless access systems including CDMA (code division multipleaccess), FDMA (frequency division multiple access), TDMA (time divisionmultiple access), OFDMA (orthogonal frequency division multiple access),SC-FDMA (single carrier frequency division multiple access) and thelike. CDMA can be implemented by such a wireless technology as UTRA(universal terrestrial radio access), CDMA 2000 and the like. TDMA canbe implemented with such a wireless technology as GSM/GPRS/EDGE (GlobalSystem for Mobile communications)/General Packet Radio Service/EnhancedData Rates for GSM Evolution). OFDMA can be implemented with such awireless technology as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, E-UTRA (Evolved UTRA), etc. UTRA is a part of UMTS (UniversalMobile Telecommunications System). 3GPP (3rd Generation PartnershipProject) LTE (long term evolution) is a part of E-UMTS (Evolved UMTS)that uses E-UTRA. The 3GPP LTE adopts OFDMA in DL and SC-FDMA in UL.And, LTE-A (LTE-Advanced) is an evolved version of 3GPP LTE.

For clarity, the following description mainly concerns 3GPP LTE/LTE-A,by which the present invention is non-limited. Specific terminologiesused in the following description are provided to help an understandingof the present invention. And, a usage of the specific terminology canbe modified into other forms that come within the scope of the appendedclaims and their equivalents.

FIG. 1 is a diagram for one example of a structure of a radio frame.

Referring to FIG. 1, a radio frame includes 10 subframes. Each of thesubframes includes 2 slots in time domain. And, a time taken to transmita subframe is defined as a transmission time interval (hereinafterabbreviated TTI). For instance, one subframe can have a length of 1 msand one slot can have a length of 0.5 ms. One slot has a plurality ofOFDM (orthogonal frequency division multiplexing) or SC-FDMA (singlecarrier frequency division multiple access) symbols in time domain. LTEuses OFDMA in DL and also uses SC-FDMA in UL. Hence, OFDM or SC-FDMAsymbol indicates one symbol duration. A resource block (hereinafterabbreviated RB) is a resource allocation unit and includes a pluralityof contiguous subcarriers in one slot. The structure of the radio frameshown in the drawing is exemplary. Optionally, the number of subframesincluded in a radio frame, the number of slots included in the subframe,and the number of symbols included in the slot can be modified byvarious schemes.

FIG. 2 is a diagram for one example of a resource grid of a DL slot.

Referring to FIG. 2, a DL slot includes a plurality of OFDM symbols intime domain. One DL slot includes 7 or 6 OFDM symbols and a resourceblock is able to include 12 subcarriers in frequency domain. Eachelement on a resource grid is named a resource element (hereinafterabbreviated RE). One RG includes 12×6 or 12×7 REs. The number N of RBsincluded in a DL slot depends on a DL transmission bandwidth. Astructure of a UL slot is similar to that of the DL slot, in which OFDMsymbol is substituted with SC-FDMA symbol.

FIG. 3 is a diagram for a structure of a DL frame.

Referring to FIG. 3, maximum 3 or 4 OFDM symbols situated in a head partof a first slot of a subframe corresponds to a control region to which acontrol channel is allocated. The rest of the OFDM symbols correspond toa data region to which PDSCH (physical downlink shared channel) isallocated. Examples of a DL control channel used by LTE include PCFICH(Physical Control Format Indicator Channel), PDCCH (Physical DownlinkControl Channel), PHICH (Physical hybrid ARQ indicator Channel) and thelike. The PCFICH is transmitted in a first OFDM symbol of a subframe andcarries an information on the number of OFDM symbols used for atransmission of a control channel within the subframe. The PHICH carriesHARQ ACK/NACK (Hybrid Automatic Repeat requestacknowledgment/negative-acknowledgment) signal in response to a ULtransmission.

The control information transmitted on PDCCH is named a downlink controlinformation (DCI). The DCI includes a resource allocation informationfor a user equipment or a user equipment group and other controlinformations. For instance, the DCI includes UL/DL schedulinginformation, UL transmission (Tx) power control command and the like.

The PDCCH carries transmission format and resource allocationinformation of DL-SCH (downlink shared channel), transmission format andresource allocation information of UL-SCH (uplink shared channel),paging information on PCH (paging channel), system information onDL-SCH, resource allocation information of such a higher layer controlmessage as a random access response transmitted on PDSCH, Tx powercontrol command set for individual UEs within a UE group, Tx powercontrol command, activation indication information of VoIP (voice overIP) and the like. A plurality of PDCCHs can be carried on the controlregion. A user equipment is able to monitor a plurality of the PDCCHs.The PDCCH is carried on an aggregation of at least one or morecontiguous CCEs (control channel elements). The CCE is a logicalallocation unit used in providing the PDCCH with a coding rate based ona radio channel status. The CCE corresponds to a plurality of REGs(resource element groups). A format of the PDCCH and the number of PDCCHbits are determined in accordance with the number of CCEs. A basestation determines a PDCCH format in accordance with a DCI which is tobe transmitted to a user equipment and attaches a CRC (cyclic redundancycheck) to a control information. The CRC is masked with an identifier(e.g., RNTI (radio network temporary identifier) in accordance with anowner of the PDCCH or a purpose of using the PDCCH. For instance, if thePDCCH is provided for a specific user equipment, an identifier (e.g.,cell-RNTI (C-RNTI) of the corresponding user equipment can be masked onthe CRC. In case that the PDCCH is provided for a paging message, apaging identifier (e.g., paging-RNTI (P-RNTI)) can be masked on the CRC.If the PDCCH is provided for system information (particularly, a systeminformation block (SIC)), the CRC may be masked with SI-RNTI (systeminformation RNTI). If the PDCCH is provided for a random accessresponse, the CRC may be masked with RA-RNTI (random access-RNTI.

FIG. 4 is a diagram for one example of a structure of a UL subframe.

Referring to FIG. 4, a UL frame includes a plurality of slots (e.g., 2slots). Each of the slots is able to include a different number ofSC-FDMA symbols in accordance with a CP length. The UL subframe can bedivided into a data region and a control region in frequency domain. Thedata region includes PUSCH and is used to transmit such a data signal asan audio and the like. The control region includes PUCCH and is used totransmit UL control information (UCI). The PUCCH includes an RB pairsituated at both ends of the data region and performs hopping on theboundary of a slot.

The PUCCH may be used to transmit the following control informations.

-   -   SR (scheduling request): This information is used to request an        uplink UL-SCH resource and is transmitted by OOK (on-off keying)        scheme.    -   HARQ ACK/NACK: This is a response signal to a DL data packet on        PDSCH. This signal indicates whether the DL data packet is        successfully received. 1-bit ACK/NACK is transmitted in response        to a single DL codeword. 2-bit ACK/NACK is transmitted in        response to two DL codewords.    -   CQI (channel quality indicator): This is feedback information on        a DL channel. MIMO-related (multiple input multiple output        related) feedback information includes RI (rank indicator), PMI        (precoding matrix indicator), PTI (precoding type indicator) and        the like. And, 20 bits per subframe are used.

A size or quantity of control information (UCI), which can betransmitted in a subframe by a user equipment, may depend on the numberof SC-FDMAs available for control information transmission. The SC-FDMAavailable for the control information transmission means SC-FDMA symbolleft after excluding SC-FDMA symbols for reference signal transmissionin subframe. In case of SRS (sounding reference signal) set subframe, alast SC-FDMA symbol of the subframe is excluded as well. A referencesignal is used for coherent detection of PUCCH. And, PUCCH supports 7formats according to transmitted information.

Table 1 shows mapping relation between PUCCH format and UCI in LTE.

TABLE 1 PUCCH Format Uplink Control Information (UCI) Format 1 SR(scheduling request) (non-modulated waveform) Format 1a 1-bit HARQACK/NACK (SR present/absent) Format 1b 2-bit HARQ ACK/NACK (SRpresent/absent) Format 2 CQI (20 coded bits) Format 2 CQI and 1- or2-bit HARQ ACK/NACK (20 bits) (extended CP corresponds only) Format 2aCQI and 1-bit HARQ ACK/NACK ((20 + 1) coded bits) Format 2b CQI and2-bit HARQ ACK/NACK ((20 + 2) coded bits)

FIG. 5 shows one example of a heterogeneous network including a macrocell and a micro cell. In the next generation communication standardsincluding 3GPP LTE-A and the like, there are ongoing discussions on aheterogeneous network in which a micro cell having a low transmissionpower exists by overlapping within a conventional macro cell coverage.

Referring to FIG. 5, a macro cell may be able to overlap with at leastone micro cells. A service of the macro cell may be provided by a macrobase station (macro eNodeB: MeNB). In this specification, a macro celland a macro eNodeB may be usable interchangeably. A user equipmentconnected to the macro cell may be called a macro user equipment (macroUE). The macro UE may receive a DL signal from the macro eNodeB andtransmit a UL signal to the macro eNodeB.

The micro cell may be called a femto cell or a pico cell. The service ofthe micro cell may be provided by one of a pico eNodeB, a home eNodeB(HeNB), a relay node (RN) and the like. For clarity and convenience ofthe following description, a pico eNodeB, a home eNodeB (HeNB), a relaynode (RN) or the like may be commonly called a home eNodeB (HeNB). Inthe present specification, the micro cell and the home eNodeB may beinterchangeably usable. A user equipment connected to a micro cell maybe called a micro user equipment or a home user equipment (home-UE). Thehome user equipment receives a downlink signal from the home eNodeB andalso transmits an uplink signal to the home eNodeB.

Micro cells may be classified into an OA (open access) cell and a CSG(closed subscriber group) cell in accordance with accessibility. Inparticular, the OA cell may mean the micro cell that enables a userequipment to receive a service at any time without separate accessrestriction if necessary. On the other hand, the CSG cell may mean themicro cell that enables a granted specific user equipment to receive aservice only.

Since a macro cell and a micro cell are3 configured to overlap with eachother in a heterogeneous network, inter-cell interference may cause aserious problem. In case that a macro user equipment is located on theboundary between a macro cell and micro cell, as shown in FIG. 5, adownlink signal of a home eNodeB may work as interference on the macrouser equipment. Similarly, a downlink signal of a macro base station maywork as interference on a home user equipment in a micro cell. Moreover,an uplink signal of a macro user equipment may work as interference on ahome eNodeB. Similarly, an uplink signal of a home user equipment maywork as interference on a macro eNodeB.

Hence, in case that a heterogeneous network is configured, a related arthome eNodeB controls it DL power by utilizing a DL signal strength of amacro eNodeB in order to secure performance of a neighbor macro userequipment and to maintain its coverage. In this case, the DL signalstrength of the macro eNodeB may be directly measured via a DL receiverof the home eNodeB. Alternatively, the DL signal strength of the macroeNodeB may be inferred from a measurement report made by a userequipment, and preferably, by a home user equipment.

Formula 1 shows one example of a DL power control method of a homeeNodeB according to a related art. In the following formula, eachparameter may be given per DL physical channel. For instance, the DLphysical channel may include one of PCFICH (Physical Control FormatIndicator Channel), PHICH (Physical hybrid ARQ indicator Channel), PDCCH(Physical Downlink Control Channel), PDSCH (Physical Downlink SharedChannel) and the like.

P _(—) tx=MEDIAN(α×P _(—) M+β, P_max, P_min)[dBm]  [Formula 1]

In Formula 1, P_tx indicates a DL transmission power of a home eNodeB oran upper limit of the DL transmission power. Hence, a real DLtransmission power of the home eNodeB may have a value equal to orsmaller than P_tx.

The P_max indicates a maximum transmission power of the home eNodeB.P_min indicates a minimum transmission power of the home eNodeB. And,each of the P_max and the P_min may be given in accordance with aphysical performance of an RF (radio frequency) module or may bearbitrarily set by a network.

The P_M indicates a strength/power of a DL signal of a macro eNodeB or avalue associated with the strength or power. For instance, the P_M mayindicates SNR (signal to noise ratio), SINR (signal to interference andnoise ratio), CIR (carrier to interference ratio), CINR (carrier tointerference and noise ratio), RSRP (reference signal received power),RSRQ (reference signal received quality) or a value associated thereof.The P_M may be obtained by measuring a reference signal of the macroeNodeB. And, the P_M may be measured or defined by a resource elementunit.

The α is a constant or a parameter (combination) for a power control.And, the β is a constant or a parameter (combination) for a powercontrol.

The MEDIAN (A, B, C) may indicate a median value of A, B and C. TheMEDIAN (A, B, C) may be represented as an equivalent formula. Forinstance, MEDIAN (A, B, C)=MAX (A, MIN (B, C))=MIN (A, MAX (B, C)). Inthis case, MAX (A, B) indicates either A or B, which is greater than theother. MIN (A, B) indicates either A or B, which is smaller than theother.

FIG. 6 shows one example of a power control method in accordance withFormula 1. In Formula 1, an upper limit P_tx of a DL transmission powerof a home eNodeB is set to be in direct proportion to P_M within apredetermined range. A value of (path loss+shadowing) for a macro eNodeBis related to P_M. If the (path loss+shadowing) value increases, the P_Mdecreases. If the (path loss+shadowing) value decreases, the P_Mincreases.

Referring to FIG. 6, as P_M increases, P_tx of a home eNodeB is sethigh. Hence, in case that the home eNodeB is located adjacent to a macroeNodeB, it may be able to protect a coverage of the home eNodeB fromstrong interference of the macro eNodeB. On the contrary, as P_Mdecreases, P_tx of a home eNodeB is set low. Hence, in case that thehome eNodeB is located remote from a macro eNodeB, it may be able tosecure performance of a macro user equipment affected by stronginterference from the home eNodeB.

Yet, according to properties of a home eNodeB generally installed at anindoor place, it may be highly probable that a DL signal of a macroeNodeB, which is measured in the vicinity of the home eNodeB, becomesconsiderably weak by passing through a wall of the correspondingbuilding. Hence, P_M obtained by the home eNodeB may become very small.In doing so, if the method according to Formula 1 applies, despite thata real DL signal strength of the macro eNodeB is high, a DL transmissionpower of the home eNodeB may be limited by a minimum transmission powerP_min. In this case, DL performance of the home eNodeB may bedeteriorated. Meanwhile, a distance between a macro eNodeB and a homeeNodeB may be set enough to avoid interference in-between. According tothe method of Formula 1, despite the low probability of inter-cellinterference, as P_M is small, a DL transmission power of the homeeNodeB may be limited by a minimum transmission power P_min. Hence, DLperformance of the home eNodeB may be deteriorated.

In order to solve the above-described problems, the present inventionproposes a method of efficiently performing a DL power control (or powersetting) of a home eNodeB in order to minimize inter-cell interferencein a heterogeneous network.

A DL power control of a home eNodeB according to the present inventionassumes that heterogeneous eNodeBs (i.e., channels of the heterogeneouseNodeBs) coexist. Therefore, the DL power control of the home eNodeBaccording to the present invention may apply only if channels of theheterogeneous eNodeBs coexist. To this end, the DL power control of thehome eNodeB according to this proposal may be limitedly applicable onlyif a strength/power (P_M) of a DL signal of a heterogeneous eNodeB(e.g., a macro eNodeB) or a value associated with the strength/power hasa value equal to or greater than a prescribed threshold at least. Inparticular, the P_M or the associated value is equal to or greater thanthe prescribed threshold, as channels of the home eNodeB and the macroeNodeB coexist, the home eNodeB may be able to use the power controlmethod proposed by the present invention. On the contrary, if the P_M orthe associated value is smaller than the prescribed threshold, as thechannels of the home eNodeB and the macro eNodeB do not coexist (i.e.,the home eNodeB is isolated from the macro eNodeB), the home eNodeB neednot perform the power control in consideration of the macro eNodeB.

According to a first embodiment of the present embodiment, if a homeeNodeB is installed in an area isolated from a signal of a macro eNodeB,although a DL signal of the macro eNodeB is considerably small, P_tx ofthe home eNodeB may be set to have a value greater than P_min. Whetherthe home eNodeB is isolated may be previously set by a network serviceprovider. Moreover, whether the home eNodeB is isolated may beindirectly inferred by measuring a DL signal of the macro eNodeB. Forinstance, if a prescribed threshold is set for the home eNodeB, the homeeNodeB may be able to determine an isolated situation for a case thatP_M, another DL signal measured value or a size of a value associatedwith the P_M or the DL signal measured value is smaller than thethreshold.

The P_M may indicate a DL signal strength of the macro eNodeB or a valueassociated with the DL signal strength. For instance, the P_M may beable to indicate SNR, SINR, CIR, CINR, RSRP, RSRQ or an associated valuethereof Hence, the P_M may be associated with a size of a path loss andshadowing from the macro eNodeB to the home eNodeB (or a home userequipment). The P_M may be directly measured via a DL receiver of thehome eNodeB. Alternatively, the P_M may be inferred from a measurementreport made by a user equipment, and preferably, by a home userequipment.

According to the present example, if a size of the P_M becomes smallerthan a threshold (e.g., if a size of a path loss and shadowing from themacro eNodeB to the home eNodeB exceeds the threshold), P_tx of the homeeNodeB may be set higher than P_min. For instance, if the size of theP_M becomes smaller than the threshold, the home eNodeB may be able tomaintain the P_tx as a predetermined value greater than the P_min. Foranother instance, if the size of the P_M becomes smaller than thethreshold, the home eNodeB may be able to adaptively increase the P_txin consideration of the size of the P_M. According to the presentembodiment, the threshold may be set to a fixed value or a valuevariable in accordance with a peripheral situation. For example, thethreshold may be set to a strength of total received DL signals (orpowers) or a value associated with the total strength. In this case, asignal (or power) of the home eNodeB may be excluded from the totalreceived DL signals (or powers).

Formulas 2 to 5 may show examples of a power control method according tothe present embodiment.

$\begin{matrix}{\mspace{20mu} {{{P\_ tx} = {{{MEDIAN}\left( {P^{\prime},{P\_ max},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}\mspace{20mu} {P^{\prime} = \left\{ {{\begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ M} \geq {Threshold}} \right) \\\gamma & \left( {{P\_ M} < {Threshold}} \right)\end{matrix}\mspace{20mu} {or}{P\_ tx}} = \left\{ \begin{matrix}{{MEDIAN}\begin{pmatrix}{{{\alpha \times {P\_ M}} + \beta},} \\\begin{matrix}{{P\_ max},} \\{P\_ min}\end{matrix}\end{pmatrix}} & \left( {{P\_ M} \geq {Threshold}} \right) \\\gamma & \left( {{P\_ M} < {Threshold}} \right)\end{matrix} \right.} \right.}}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Formula 2, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. And, γ indicates a constant ora parameter (combination) for a power control (γ>P_min).

$\begin{matrix}{\mspace{20mu} {{{P\_ tx} = {{{MEDIAN}\left( {P^{\prime},{P\_ max},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}{P^{\prime} = \left\{ \begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ M} \geq {{Threshold\_}1}} \right) \\\gamma_{1} & \left( {{{Threshold\_}2} \leq {P\_ M} < {{Threshold\_}1}} \right) \\\gamma_{2} & \left( {{{Threshold\_}3} \leq {P\_ M} < {{Threshold\_}2}} \right) \\\vdots & \; \\\gamma_{n} & \left( {{P\_ M} < {Threshold\_ n}} \right)\end{matrix} \right.}}} & \left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack \\{\mspace{20mu} {or}} & \; \\{{P\_ tx} = \left\{ \begin{matrix}{{MEDIAN}\begin{pmatrix}{{{\alpha \times {P\_ M}} + \beta},} \\\begin{matrix}{{P\_ max},} \\{P\_ min}\end{matrix}\end{pmatrix}} & \left( {{P\_ M} \geq {{Threshold\_}1}} \right) \\\gamma_{1} & \begin{pmatrix}{{{Threshold\_}2} \leq} \\{{P\_ M} < {{Threshold\_}1}}\end{pmatrix} \\\gamma_{2} & \begin{pmatrix}{{{Threshold\_}3} \leq} \\{{P\_ M} < {{Threshold\_}2}}\end{pmatrix} \\\vdots & \; \\\gamma_{n} & \left( {{P\_ M} < {Threshold\_ n}} \right)\end{matrix} \right.} & \;\end{matrix}$

In Formula 3, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. And, γ₁, γ₂, . . . γ_(n)indicate constants or parameters (combinations) for a power control(P_min<γ₁<γ₂< . . . <Y_(n)).

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\left( {P^{\prime},{P\_ max},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}{P^{\prime} = \left\{ \begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ M} \geq {Threshold}} \right) \\{{\alpha^{\prime} \times \left( {A - {\kappa \times {P\_ M}}} \right)} + \beta^{\prime}} & \left( {{P\_ M} < {Threshold}} \right)\end{matrix} \right.}} & \left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Formula 4, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. The α′, β′ and κ′ indicateconstants or parameters (or combinations) for a power control,respectively. Moreover, the A indicates a constant or a parameter(combination) for a power control.

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\left( {P^{\prime},{P\_ max},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}{P^{\prime} = \left\{ \begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ M} \geq {Threshold}} \right) \\{{\alpha^{\prime} \times \frac{1}{P\_ M}} + \beta^{\prime}} & \left( {{P\_ M} < {Threshold}} \right)\end{matrix} \right.}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Formula 5, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. The α′ and β′ indicateconstants or parameters (or combinations) for a power control,respectively.

FIG. 7 shows a power control method according to a 1^(st) embodiment ofthe present invention. Referring to FIG. 7( b), if a size of a path lossand shadowing exceeds a threshold, as the size of the path loss andshadowing increases, P_tx of a home eNodeB is maintained at a levelhigher than P_min. On the contrary, referring to FIG. 7( a), if a sizeof a path loss and shadowing exceeds a threshold, as the size of thepath loss and shadowing increases, P_tx of a home eNodeB is raised at apredetermined rate. This is exemplary. After the threshold, as the sizeof the path loss and shadowing increases, P_tx may increase step bystep. After the size of the path loss and shadowing has been dividedinto several intervals, as the size of the path loss and shadowingbecomes greater than the threshold, the P_tx may be raised at a rategiven to each of the intervals.

In a second embodiment of the invention, a home eNodeB measures ULinterference on neighbor macro user equipments via a UL receiver andknows a presence/distance of a macro user equipment located in aneighbor area through a UL interference size. For instance, if a size ofthe UL interference becomes greater than a predetermined threshold, itmay be able to determine that a macro user equipment exists in thevicinity of the home eNodeB. In this case, in order to secureperformance of the macro user equipment receiving interference from thehome eNodeB, it may be necessary to control a DL power of the homeeNodeB.

Therefore, the present example proposes to perform a DL power control ofa home eNodeB in consideration of a UL interference size measured by thehome eNodeB. In particular, if UL interference exceeds a predeterminedthreshold, the home eNodeB determines that a macro user equipment existsin a neighbor area and may be then able to set P_tx of the home eNodeBto have a value smaller than P max. For instance, if the UL interferencesize exceeds the threshold, the home eNodeB may be able to maintain theP_tx as a predetermined value smaller than the P_max. For anotherinstance, if the UL interference exceeds a predetermined threshold, thehome eNodeB may be able to adaptively lower the P_tx in consideration ofa size of the UL interference.

The size P_UL of the UL interference may be obtained using variousmethods known to the public in the corresponding field. For instance,the size P_UL of the UL interference may be obtainable using astrength/power of a UL signal of a macro user equipment or a valueassociated with the strength/power. In particular, the size P_UL of theUL interference may be obtained from SNR, SINR, CINR, RSRP, RSRQ or anassociated value thereof The P_UL may be obtained by measuring areference signal of a macro user equipment. The P_UL may bemeasured/defined by a resource element unit. According to the presentembodiment, the threshold may be set to a fixed value or a valuevariable in accordance with a peripheral situation. For example, thethreshold may be set to a strength of total received UL signals (orpowers) or a value associated with the total strength. In this case, asignal (or power) of the home eNodeB may be excluded from the totalreceived UL signals (or powers).

Formulas 6 to 9 may show examples of a power control method according tothe present embodiment.

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\left( {P^{\prime},{P\_ max},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}P^{\prime} = \left\{ {{\begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ UL} < {Threshold}} \right) \\\gamma & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix}{or}P^{\prime}} = \left\{ \begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ UL} < {Threshold}} \right) \\{{\alpha \times {P\_ M}} + \beta - \gamma^{\prime}} & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix} \right.} \right.} & \left\lbrack {{Formula}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In Formula 6, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. P_UL indicates a ULinterference size measured from a user equipment (e.g., a macro userequipment) or a value associated with the UL interference size. And, γindicates a constant or a parameter (combination) for a power control(γ<P_max). Moreover, γ′ indicates a constant or a parameter(combination) for a power control.

$\begin{matrix}{\mspace{20mu} {{{P\_ tx} = {{{MEDIAN}\left( {P^{\prime},{P\_ max},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}{P^{\prime} = \left\{ \begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ M} \geq {{Threshold\_}1}} \right) \\\gamma_{1} & \left( {{{Threshold\_}2} \leq {P\_ M} < {{Threshold\_}2}} \right) \\\gamma_{2} & \left( {{{Threshold\_}3} \leq {P\_ M} < {{Threshold\_}3}} \right) \\\vdots & \; \\\gamma_{n} & \begin{pmatrix}{{Threshold\_ n} \leq} \\{{P\_ UL} < {{Threshold\_ n} + 1}}\end{pmatrix}\end{matrix} \right.}}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack \\{\mspace{20mu} {or}} & \; \\{P^{\prime} = \left\{ \begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ UL} \geq {{Threshold\_}1}} \right) \\{{\alpha \times {P\_ M}} + \beta - \gamma_{1}^{\prime}} & \begin{pmatrix}{{{Threshold\_}1} \leq} \\{{P\_ M} < {{Threshold\_}2}}\end{pmatrix} \\{{\alpha \times {P\_ M}} + \beta - \gamma_{2}^{\prime}} & \begin{pmatrix}{{{Threshold\_}2} \leq} \\{{P\_ M} < {{Threshold\_}3}}\end{pmatrix} \\\vdots & \; \\{{\alpha \times {P\_ M}} + \beta - \gamma_{n}^{\prime}} & \begin{pmatrix}{{Threshold\_ n} \leq} \\{{P\_ UL} < {{Threshold\_ n} + 1}}\end{pmatrix}\end{matrix} \right.} & \;\end{matrix}$

In Formula 7, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. P_UL indicates a ULinterference size measured from a user equipment (e.g., a macro userequipment) or a value associated with the UL interference size. And, γ₁,γ₂, . . . γ_(n) indicate constants or parameters (combinations) for apower control (P_max>γ₁>γ₂> . . . >γ_(n)). Moreover, And, γ′₁, γ′², . .. γ′_(n) indicate constants or parameters (combinations) for a powercontrol (γ′₁<γ′₂< . . . γ′_(n)).

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\left( {P^{\prime},{P\_ max},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}{P^{\prime} = \left\{ {{\begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ UL} < {Threshold}} \right) \\{\left( {A - {\alpha^{\prime} \times {P\_ UL}}} \right) + \beta^{\prime}} & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix}{or}P^{\prime}} = \left\{ \begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ UL} < {Threshold}} \right) \\\begin{matrix}{{\alpha \times {P\_ M}} + \beta -} \\{\alpha^{\prime} \times {P\_ UL}}\end{matrix} & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix} \right.} \right.}} & \left\lbrack {{Formula}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In Formula 8, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. The α′ and β′ indicateconstants or parameters (or combinations) for a power control,respectively. The A indicates a constant or a parameter (combination)for a power control. And, the P_UL indicates a UL interference sizemeasured from a user equipment (e.g., a macro user equipment) or a valueassociated with the UL interference size.

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\left( {P^{\prime},{P\_ max},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}{P^{\prime} = \left\{ \begin{matrix}{{\alpha \times {P\_ M}} + \beta} & \left( {{P\_ UL} < {Threshold}} \right) \\{{\alpha^{\prime} \times \frac{P\_ M}{P\_ UL}} + \beta^{\prime}} & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix} \right.}} & \left\lbrack {{Formula}\mspace{14mu} 9} \right\rbrack\end{matrix}$

In Formula 9, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. The α′ and β′ indicateconstants or parameters (or combinations) for a power control,respectively. And, the P_UL indicates a UL interference size measuredfrom a user equipment (e.g., a macro user equipment) or a valueassociated with the UL interference size.

FIG. 8 shows one example of a power control method according to a 2^(nd)embodiment of the present invention. The present example assumes asituation of ‘P_tx=P_max’ if a UL interference size is smaller than athreshold. Referring to FIG. 8 (a), if a size of UL interference exceedsa threshold, as the size of the UL interference increases, P_tx of ahome eNodeB is maintained small at a predetermined level. On thecontrary, referring to FIG. 8( b), if a size of UL interference exceedsa threshold, as the size of the UL interference increases, P_tx of ahome eNodeB is lowered at a predetermined rate. This is exemplary. Afterthe threshold, as the size of the UL interference increases, P_tx may belowered step by step. After the size of the UL interference has beendivided into several intervals, as the size of the UL interferencebecomes greater than the threshold, the P_tx may be lowered at a rategiven to each of the intervals.

According to the above-described example, proposed is a method ofadaptively controlling the parameter α×P_M+β(=P′) shown in Formula 1 inconsideration of a UL interference size. This is just exemplary.Alternatively, it may be able to consider controlling the P_max ofFormula 1 in consideration of a UL interference size. In particular, ifUL interference exceeds a predetermined threshold, the home eNodeBdetermines that a macro user equipment exists in a neighbor area and maybe then able to set P_max of the home eNodeB to have a value smallerthan an original value. For instance, if the UL interference sizeexceeds the threshold, the home eNodeB may be able to maintain the P_txas a predetermined value smaller than the original value. For anotherinstance, if the UL interference exceeds a predetermined threshold, thehome eNodeB may be able to adaptively lower the P_max in considerationof a size of the UL interference.

Formulas 10 to 13 may show examples of a power control method accordingto the present embodiment.

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\left( {{{\alpha \times {P\_ M}} + \beta},{P^{\prime}{\_ max}},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}\mspace{20mu} {{P^{\prime}{\_ max}} = \left\{ {{\begin{matrix}{P\_ max} & \left( {{P\_ UL} < {Threshold}} \right) \\\gamma & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix}\mspace{20mu} {or}\mspace{20mu} P^{\prime}{\_ max}} = \left\{ \begin{matrix}{P\_ max} & \left( {{P\_ UL} < {Threshold}} \right) \\{{P\_ max} - \gamma^{\prime}} & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix} \right.} \right.}} & \left\lbrack {{Formula}\mspace{14mu} 10} \right\rbrack\end{matrix}$

In Formula 10, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. P UL indicates a ULinterference size measured from a user equipment (e.g., a macro userequipment) or a value associated with the UL interference size. And, γindicates a constant or a parameter (combination) for a power control(γ<P_max). Moreover, γ′ indicates a constant or a parameter(combination) for a power control.

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\begin{pmatrix}{{{\alpha \times {P\_ M}} + \beta},} \\{{P^{\prime}{\_ max}},{P\_ min}}\end{pmatrix}}\lbrack{dBm}\rbrack}}{P^{\prime}{\_ max}} = \left\{ \begin{matrix}{P\_ max} & \left( {{P\_ UL} \geq {{Threshold\_}1}} \right) \\\gamma_{1} & \begin{pmatrix}{{{Threshold\_}1} \leq} \\{{P\_ M} < {{Threshold\_}2}}\end{pmatrix} \\\gamma_{2} & \begin{pmatrix}{{{Threshold\_}2} \leq} \\{{P\_ M} < {{Threshold\_}3}}\end{pmatrix} \\\vdots & \; \\\gamma_{n} & \begin{pmatrix}{{Threshold\_ n} \leq} \\{{P\_ UL} < {{Threshold\_ n} + 1}}\end{pmatrix}\end{matrix} \right.} & \left\lbrack {{Formula}\mspace{14mu} 11} \right\rbrack \\{or} & \; \\{{P^{\prime}{\_ max}} = \left\{ \begin{matrix}{P\_ max} & \left( {{P\_ UL} \geq {{Threshold\_}1}} \right) \\{{P\_ max} - \gamma_{1}^{\prime}} & \begin{pmatrix}{{{Threshold\_}1} \leq} \\{{P\_ UL} < {{Threshold\_}2}}\end{pmatrix} \\{{P\_ max} - \gamma_{2}^{\prime}} & \begin{pmatrix}{{{Threshold\_}2} \leq} \\{{P\_ UL} < {{Threshold\_}3}}\end{pmatrix} \\\vdots & \; \\{{P\_ max} - \gamma_{n}^{\prime}} & \begin{pmatrix}{{Threshold\_ n} \leq} \\\begin{matrix}{{P\_ UL} <} \\{{Threshold\_ n} + 1}\end{matrix}\end{pmatrix}\end{matrix} \right.} & \;\end{matrix}$

In Formula 11, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. P_UL indicates a ULinterference size measured from a user equipment (e.g., a macro userequipment) or a value associated with the UL interference size. And, γ₁,γ₂, . . . γ_(n) indicate constants or parameters (combinations) for apower control (P_max>γ₁>γ₂> . . . >γ_(n) ). Moreover, And, γ′₁, γ′₂, . .. , γ′_(n) indicate constants or parameters (combinations) for a powercontrol (γ′₁<γ′₂< . . . <γ′_(n)).

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\left( {{{\alpha \times {P\_ M}} + \beta},{P^{\prime}{\_ max}},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}{P^{\prime}{\_ max}} = \left\{ {\begin{matrix}{P\_ max} & \left( {{P\_ UL} < {Threshold}} \right) \\{\left( {A - {\alpha^{\prime} \times {P\_ UL}}} \right) + \beta^{\prime}} & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix}\mspace{20mu} {or}} \right.} & \left\lbrack {{Formula}\mspace{14mu} 12} \right\rbrack \\{{P^{\prime}{\_ max}} = \left\{ \begin{matrix}{P\_ max} & \left( {{P\_ UL} < {Threshold}} \right) \\{{P\_ max} - {\alpha^{\prime} \times {P\_ UL}}} & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix} \right.} & \;\end{matrix}$

In Formula 12, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. The α′ and β′ indicateconstants or parameters (or combinations) for a power control,respectively. The A indicates a constant or a parameter (combination)for a power control. And, the P_UL indicates a UL interference sizemeasured from a user equipment (e.g., a macro user equipment) or a valueassociated with the UL interference size.

$\begin{matrix}{{{P\_ tx} = {{{MEDIAN}\left( {{{\alpha \times {P\_ M}} + \beta},{P^{\prime}{\_ max}},{P\_ min}} \right)}\lbrack{dBm}\rbrack}}{{P^{\prime}{\_ max}} = \left\{ {\begin{matrix}{P\_ max} & \left( {{P\_ UL} < {Threshold}} \right) \\{{\alpha^{\prime} \times \frac{P\_ max}{P\_ UL}} + \beta^{\prime}} & \left( {{P\_ UL} \geq {Threshold}} \right)\end{matrix}.} \right.}} & \left\lbrack {{Formula}\mspace{14mu} 13} \right\rbrack\end{matrix}$

In Formula 13, P_tx, P_max, P_min, P_M, α, β and MEDIAN (A, B, C) areidentical to those defined in Formula 1. The α′ and β′ indicateconstants or parameters (or combinations) for a power control,respectively. And, the P_UL indicates a UL interference size measuredfrom a user equipment (e.g., a macro user equipment) or a valueassociated with the UL interference size.

For clarity and convenience, although the 1^(st) embodiment and the2^(nd) embodiment are independently described, they may be combinedtogether. For instance, the parameter α×P_M+β(=P′) in Formula 1 may becontrolled in consideration of both a signal strength (e.g., P_M) and aUL interference (P_UL) of a macro eNodeB. For another instance, P_max iscontrolled like Formulas 10 to 13 in consideration of a UL interferencesize and P′ of a home eNodeB may be controlled like Formulas 2 to 5 inconsideration of a signal strength (e.g., P_M) of a macro eNodeB.

Moreover, a home eNodeB may be able to apply the above-mentioned DLpower control methods in a manner of combining the methods in accordancewith a presence or non-presence of a home user equipment. For instance,only if a measurement report made by the home user equipment exists, theDL transmission power control method according to the 1^(st) embodimentof the present invention may be applied. On the contrary, if ameasurement report made by the home user equipment does not exist, P_txof the home eNodeB may be set to a previously determined default valueor a value according to Formula 1.

FIG. 9 is a diagram for one example of a base station (eNodeB) and auser equipment applicable to one embodiment of the present invention. Inthis case, the base station may include a macro base station or a homebase station. Similarly, the user equipment may include a macro userequipment or a home user equipment. In case that a relay is included ina wireless communication system, a communication is performed between abase station and a relay in a backhaul link or a communication isperformed between a relay and a user equipment in an access link.Therefore, the base station or user equipment shown in the drawing canbe substituted with the relay to cope with a given situation.

Referring to FIG. 9, a wireless communication includes a base station(BS) 110 and a user equipment (UE) 120. The base station 100 includes aprocessor 112, a memory 114 and a radio frequency (RF) unit 116. Theprocessor 112 can be configured to implement the procedures and/ormethods proposed by the present invention. The memory 114 is connectedto the processor 112 and stores various kinds of informations related tooperations of the processor 112. The RF unit 116 is connected to theprocessor 112 and transmits and/or receives radio signals. The userequipment 120 includes a processor 122, a memory 124 and an RF unit 126.The processor 122 can be configured to implement the procedures and/ormethods proposed by the present invention. The memory 124 is connectedto the processor 122 and stores various kinds of informations related tooperations of the processor 122. The RF unit 126 is connected to theprocessor 122 and transmits and/or receives radio signals. The basestation 110 and/or the user equipment 120 may have a single antenna or amulti-antenna.

The above-described embodiments correspond to combinations of elementsand features of the present invention in prescribed forms. And, it isable to consider that the respective elements or features are selectiveunless they are explicitly mentioned. Each of the elements or featurescan be implemented in a form failing to be combined with other elementsor features. Moreover, it is able to implement an embodiment of thepresent invention by combining elements and/or features together inpart. A sequence of operations explained for each embodiment of thepresent invention can be modified. Some configurations or features ofone embodiment can be included in another embodiment or can besubstituted for corresponding configurations or features of anotherembodiment. And, it is apparently understandable that an embodiment isconfigured by combining claims failing to have relation of explicitcitation in the appended claims together or can be included as newclaims by amendment after filing an application.

In this disclosure, embodiments of the present invention are describedcentering on the data transmission/reception relations between a basestation and a terminal. In this disclosure, a specific operationexplained as performed by a base station can be performed by an uppernode of the base station in some cases. In particular, in a networkconstructed with a plurality of network nodes including a base station,it is apparent that various operations performed for communication witha terminal can be performed by a base station or other networks exceptthe base station. In this case, ‘base station’ can be replaced by such aterminology as a fixed station, a Node B, an eNode B (eNB), an accesspoint and the like. And, ‘terminal’ can be replaced by such aterminology as a user equipment (UE), a mobile station (MS), a mobilesubscriber station (MSS)’ and the like.

Embodiments of the present invention can be implemented using variousmeans. For instance, embodiments of the present invention can beimplemented using hardware, firmware, software and/or any combinationsthereof In the implementation by hardware, a method according to eachembodiment of the present invention can be implemented by at least oneselected from the group consisting of ASICs (application specificintegrated circuits), DSPs (digital signal processors), DSPDs (digitalsignal processing devices), PLDs (programmable logic devices), FPGAs(field programmable gate arrays), processor, controller,microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code is stored in amemory unit and is then drivable by a processor. The memory unit isprovided within or outside the processor to exchange data with theprocessor through the various means known to the public.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

As mentioned in the foregoing description, the present invention isapplicable to such a wireless communication device as a user equipment,a relay, a base station and the like.

What is claimed is:
 1. A method for performing power control by a firstbase station in a wireless communication system, the method comprising:acquiring a parameter value related with signal strength of a secondbase station; determining an upper power limit of the first base stationin consideration of the signal strength of the second base station; andperforming signal transmission in consideration of the upper power limitof the first base station, wherein if a first condition(s) includingthat the parameter value is equal to or more than a first thresholdvalue is satisfied, the upper power limit of the first base station isgiven as an intermediate value among a minimum power value, a maximumpower value, and a power control value proportional to the signalstrength of the second base station, and wherein if a secondcondition(s) including that the parameter value is less than the firstthreshold value is satisfied, the upper power limit of the first basestation is given as a pre-determined value related with the transmitpower of the first base station.
 2. The method of claim 1, wherein theparameter value indicates reference signal received power measured by aresource element unit.
 3. The method of claim 1, wherein the firstthreshold value is determined based on total received power excluding asignal of the first base station.
 4. The method of claim 1, wherein theacquiring the parameter value includes receiving a measurement report onsignals of the second base station from a user equipment.
 5. The methodof claim 1, wherein the acquiring the parameter value includes measuringsignals of the second base station at the first base station.
 6. Themethod of claim 1, wherein the power control value (P′) is given byfollowing Equation:P′α=P _(—) M+β where, P_M represents a parameter value related with thesignal strength of the second base station, α represents a positivevalue, and β represents a correction value for power control.
 7. Themethod of claim 1, wherein if a value indicating uplink signal strengthof a macro user equipment is equal to or more than a second thresholdvalue, the power control value is decreased in consideration the uplinksignal strength, and wherein if the value indicating the uplink signalstrength of the macro user equipment is less than the second thresholdvalue, the power control value is maintained as it is.
 8. The method ofclaim 1, wherein if a value indicating uplink signal strength of a macrouser equipment is equal to or more than a second threshold value, themaximum power value is decreased in consideration of the uplink signalstrength, and wherein if the value indicating the uplink signal strengthof the macro user equipment is less than the second threshold value, themaximum power value is maintained as it is.
 9. A first base stationconfigured to perform power control in a wireless communication system,the first base station comprising: a radio frequency (RF) unit; and aprocessor, wherein the processor is configured to: acquire a parametervalue related with signal strength of a second base station, anddetermine an upper power limit of the first base station inconsideration of the signal strength of the second base station, whereinif a first condition(s) including that the parameter value is equal toor more than a first threshold value is satisfied, the upper power limitof the first base station is given as an intermediate value among aminimum power value, a maximum power value, and a power control valueproportional to the signal strength of the second base station, andwherein if a second condition(s) including that the parameter value isless than the first threshold value is satisfied, the upper power limitof the first base station is given as a pre-determined value relatedwith the transmit power of the first base station.
 10. The first basestation of claim 9, wherein the parameter value indicates referencesignal received power measured by a resource element unit.
 11. The firstbase station of claim 9, wherein the first threshold value is determinedbased on total received power excluding a signal of the first basestation.
 12. The first base station of claim 9, wherein the acquiringthe parameter value includes receiving a measurement report on signalsof the second base station from a user equipment.
 13. The first basestation of claim 9, wherein the acquiring the parameter value includesmeasuring signals of the second base station at the first base station.14. The first base station of claim 9, wherein the power control value(P′) is given by following Equation:P′α=P _(—) M+β where, P_M represents a parameter value related with thesignal strength of the second base station, α represents a positivevalue, and β represents a correction value for power control.
 15. Thefirst base station of claim 9, wherein if a value indicating uplinksignal strength of a macro user equipment is equal to or more than asecond threshold value, the power control value is decreased inconsideration of the uplink signal strength, and wherein if the valueindicating the uplink signal strength of the macro user equipment isless than the second threshold value, the power control value ismaintained as it is.
 16. The first base station of claim 9, wherein if avalue indicating uplink signal strength of a macro user equipment isequal to or more than a second threshold value, the maximum power valueis decreased in consideration of the uplink signal strength, and whereinif the value indicating the uplink signal strength of the macro userequipment is less than the second threshold value, the maximum powervalue is maintained as it is.